There is a need to provide an economical possibility for deliberate attenuation of determined wavelengths in a wavelength mixture of a TEM00 laser beam while maintaining beam quality and relinquishing velocity.
An effective possibility for meeting this need consists in that the laser beam is split spectrally by a dispersive element, spots are generated by a lens from the various wavelengths on a concave mirror, the beam is sent back again through the lens and dispersive element so as to be deflected at a small angle, and a polarization-preserving single-mode light-conducting fiber is arranged behind the dispersive element.
In the vicinity of the spots, individual knife edges are inserted into the beam path of the different wavelengths. These knife edges can be displaced individually and in a specific manner so that the beam can be continuously attenuated in a wavelength-selective manner and with theoretically infinitely small steps.
The movement of the knife edges can be carried out, for example, via cams and levers by stepper motors or piezoelectric bending strips.
The diffraction at the knife edges changes the beam profile. This beam profile is cleaned up again by coupling into a single-mode fiber, so that a more or less attenuated laser beam with TEM00 quality is present at the fiber output.
It is further advantageous that the dispersive element is constructed as a prism and the entrance faces and exit faces of the prism are arranged in the polarized laser beam at the Brewster angle to prevent reflection losses.
Because of the usual orientation of the polarization plane, it is advantageous to rotate it by 90xc2x0 by means of a suitable arrangement of two mirrors in order to achieve a small overall height of this arrangement and, therefore, optimum stability.